Wondered that myself Frank ... I'd be very interested to know. Perhaps
habitat type? Big Carine Swamp and Herdsman have similar layout, large water
expanses, surrounded by paperbarks and large areas of bullrushes in open
water. Could have to do with water depth/salinity. I have not visited the
southern end of Big Carine Swamp since the Reid Hwy went thru, however
driving past I've seen a lot of the area that was once intermittent pools
had been taken over by grass and weeds - could be due to change in water
regime or perhaps just natural drying out of the lake? Maybe there is
something to do with water depth and/or prefered feeding habitat/food source
of Freckled Ducks? Some of the other lakes along the Swan to Yanchup
waterways share the same features but no sightings of Freckled Duck. You
would have to look at what features Herdsman and Carine have over the other
lakes in the area. Or maybe we are just not looking hard enough? A long-shot
but perhaps amature birdos confusing/recording non-breeding freckled duck
with female Blue-bills - if people do not think it likely that such a rare
bird will occur in the area, their logic will bring them to a more suitable
conclusion? As for the southern lakes, migration routes of the Freckled Duck
may not bring them into the metro area via these lakes - so you would have
to investigate their patterns of movement (where are they coming from and
how are they getting here).
Sounds like a good idea for a project to me??? Let me know if you have any
more ideas ...
ta,
Claire
www.birdsofperth.com
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